The growth of automation in avionics, both civilian and military, is leading crews to make ever more use of electronic systems, and to have ever less direct influence on the aircraft's primary piloting controls. This automation makes it possible to decrease piloting risks and to standardize notably conventional flight procedures.
This trend has been accentuated with the generalization of flight management systems such as FMS, the acronym standing for Flight Management System.
A flight management system comprises various functional components which allow the crew to programme a flight using a navigation database. The system then computes a lateral and vertical trajectory making it possible to reach the destination of the flight plan. These computations are based on the characteristics of the aircraft and data provided by the crew and the environment of the system. The positioning and guidance functions collaborate to help the aircraft to remain on this trajectory.
The interface functions for interfacing with the crew and with the ground make it possible to put a human into the navigation loop since he alone is responsible for the progress of the flight.
In a flight management system, the pilot programmes his climb procedure into his FMS system. Certain procedures contain climb waiting circuits, termed “ascents”, to guarantee the aircraft margins in relation to the relief or conflicting traffic.
Certain airports are enclosed or require that an aircraft taking off should attain a certain setpoint altitude before beginning its cruising flight. The aircraft is therefore piloted in such a way that it flies an altitude climb circuit, the circuit being predefined and more often than not standardized.
More often than not the climb circuits have the form of a substantially helical trajectory comprising a certain number of portions of trajectories, whose 2D projections at constant altitude represent racetrack shapes, on which the aircraft climbs in a spiral.
The aircraft climbs in a spiral trajectory, the projection of whose complete waiting climb circuit represents a series of concentric racetracks. In aeronautical terminology these racetracks are also called HOLDs and it possesses geometric characteristics specific to the aircraft.
In the subsequent description either the substantially helical 3D trajectory portion whose 2D projection forms a racetrack or the 2D projection itself forming a racetrack, will be called a HOLD.
The aircraft is taken to a predefined altitude on a climb circuit, the latter comprising a certain number of HOLDs, the last of which is called the exit HOLD. Each HOLD comprises an entry point and an exit point, generally these points are the same, also called the lock-on point. The aircraft terminates its climb circuit by passing over the lock-on point.
In aeronautical terminology, it is also said that a point is sequenced from the point of view of the computer of the FMS when it is traversed by the aircraft.
FIG. 1 represents a climb circuit 11 flown by an aircraft 2 after a takeoff on a landing runway 1.
The landing runway is situated at an altitude ALT0. In this typical case, the aircraft must travel the climb circuit 11 so as to attain a setpoint altitude ALT3 allowing it to reach its cruising trajectory 9.
A first trajectory portion 3 allows the aircraft 2 to reach a zone in which the climb circuit 11 is situated. The climb circuit 11 comprises a succession of spirals 5, 7, 7′ of substantially helical form allowing the aircraft to reach the setpoint altitude and to exit the climb circuit thereafter.
Each spiral comprises an entry point and an exit point 10, 10′, 12, 12′ which have the same coordinates in latitude and in longitude.
The spirals when they are projected at constant altitude have the form of racetracks 6, 8.
The entry point to the first HOLD 5 is the point 10, the exit point from the first HOLD 5 is the point 10′. The entry point to the second HOLD 7′ is the point 12, the exit point from the second HOLD 7′ is the point 12′.
A transition trajectory portion 7 allows the aircraft to join the first HOLD to the second HOLD, the first HOLD having a smaller circumference than the second HOLD, the aircraft widens its trajectory during its climb by passing from one HOLD to another.
The aircraft leaves the last HOLD, called the exit HOLD, at the point 12′ so as to continue its climb or reach a cruising trajectory 9.
The points 12 and 12′ have the same latitude and the same longitude. Likewise the points 10 and 10′ have the same latitude and the same longitude.
It is understood in FIG. 1 that when the aircraft 2 has attained its setpoint altitude ALT3 corresponding to the altitude of the racetrack 8, it must nonetheless travel a constant-altitude trajectory portion of the exit HOLD in order to reach the lock-on point 12′ before exiting the climb circuit.
The trajectory of a climb circuit is generally generated automatically using the computer of an FMS. The pilot enters the aircraft parameters so as to compute the arrival point at the setpoint altitude allowing the aircraft to exit the climb circuit.
Aerial standards require that the aircraft must pass through the lock-on point of the climb circuit before reaching its cruising trajectory.
A problem with this type of automatic trajectory generation is that it is not optimized, the aircraft more often than not arrives in the exit HOLD at the desired altitude well before traversing the lock-on point. This constraint makes it neccesary to needlessly fly portions of the climb circuit at the required altitude before attaining the lock-on point.
Nonetheless, certain solutions exist for reducing costs and needless fuel expenditure when flying a constant-altitude waiting or climb circuit. The most direct means is to decrease the needless trajectory portions through the intervention of the pilot so as to reach the lock-on point as rapidly as possible once the exit setpoint has been attained. In a climb circuit, generally the exit setpoint is an altitude setpoint, but when overflying a waiting HOLD with a view to landing, it may involve a time setpoint for example.
Among the procedures that it must be possible to adjust to decrease the needless trajectories is the adjustment of the waiting circuits.
Honeywell's patent US2004122567 proposes that the size of a waiting circuit be adjusted manually in a reactive manner, within the framework of a particular procedure, called IMMEDIATE EXIT.
This patent comprises two drawbacks. First of all it is reactive, that is to say the method for optimizing the waiting circuit is performed during overflight thereof, it is necessary for the aircraft to be in a condition of flight of the waiting circuit in order to modify this portion. The method is therefore not predictive, thereby constituting a limitation in the adaptation of the aircraft's trajectory so as to exit the waiting circuit. Moreover this patent does not deal with circuits having ascent or descent trajectories, furthermore it deals with exit optimization for manually flown racetracks.
The applicant has also filed French patent application FR 2915824. This document describes a method for optimizing a waiting circuit. In the waiting phase the aircraft execute successive racetrack-shaped trajectories at isoaltitude during a waiting time D indicated by the air traffic control. These racetrack-shaped trajectories are predetermined in the computer and have an identical circumference. This method makes it possible to modify the size of the last predetermined trajectory so that the end of execution of a trajectory corresponds to the indicated end-of-waiting time. This method computes a whole number of trajectories that are predetermined in a time constraint. As a function of the flight time remaining (less than the time to execute a whole trajectory), the method computes a new exit trajectory that is less than a whole predetermined trajectory, either a circle, or one or two racetracks whose branches have been modified.
However, this method does not make it possible to solve the problem of optimizing an ascent circuit for the following reasons. Firstly, the ascent circuit necessarily comprises transition trajectories between the spirals whose projection on a horizontal plane forms the HOLDs. Secondly, in an ascent circuit the aircraft executes spirals whose projections on an isoaltitude plane form a HOLD but it does not travel a HOLD trajectory. Thirdly, the HOLDs of the ascent circuit are not all of equal periphery.
In so far as the objective of the climb circuit is to allow the aircraft to attain a setpoint altitude, the trajectory portion of the last lap which the aircraft turns at constant altitude is of no benefit except to bring the aircraft back to the lock-on point so as to exit this segment.
Today, the problem is not solved, the climb circuit is not optimized and the aircraft exits the climb circuit only when the lock-on point is sequenced. Drawbacks are that the aircraft loses time and fuel in looping around its climb circuit before reaching a cruising trajectory.